An electric motor is an electromagnetic/mechanical device that converts electrical energy into mechanical energy. Conversely an electrical generator is an electromagnetic/mechanical device that converts mechanical energy into electrical energy. Electrical machines such as motors and generators operate through the interaction of magnetic fields and current carrying conductors generate the force or electricity respectively. Electric motors are found in applications as diverse as pumps, blowers, fans, machine tools, household appliances, power tools, disc drives in computers and the like. Electrical motors come in various sizes from small motors that are utilized in watches to rather large electric motor/generators utilized in locomotive engines.
A rotor of an electric motor is typically the rotating part of the motor and it rotates because the magnetic fields are arranged in the motor so that torque is developed about the axis of the rotor. Electrical systems typically include electrical power generators and motors which have permanent magnet or electromagnetic rotors. Heat is generated in the rotor due to the changing magnetic fields, which are present in the rotor causing the temperature to rise in the rotor. It is desirable to cool the rotor to protect the magnets or electromagnets from damage and to increase the electrical machine power density to allow for more power from a smaller physically sized electric motor.
Conventional cooling methods include convective air or oil circulation through the motor. A rotor cooling structure is illustrated in U.S. Pat. No. 5,283,488 in which a cylindrically shaped heat pipe is used to cool a rotor. The heat pipe has an internal vapor chamber with an evaporator end, a condenser end and a plurality of radial fins regularly spaced on the periphery of the heat pipe. Each fin defines an internal chamber communicating with and extending radially from a vapor chamber. A vaporizable liquid is disposed within the heat pipe and the heat exchanger is in thermal contact with a condenser end of the heat pipe.
It is also known to cool a rotor by utilizing cooling holes having a shape that is convex that goes through the rotor, as shown in U.S. Pat. No. 7,705,503, wherein the cooling holes are arranged having a predefined spacing from the paired permanent magnets. Coolant flows through the cooling holes to remove the heat conducted thereto.
The problem with the cooling method of the cited art is that they do not cool the rotor as effectively as needed.
What is needed in the art is an efficient cooling method and apparatus for directly cooling the magnets or electromagnets of an electric motor.